1. Field of the Invention
This invention relates to the field of micro-electromechanical devices, and particularly to the structure and spring constants of conductive flexures for such devices.
2. Description of the Related Art
Micro-electromechanical (MEM) devices rely on the motion of one or more micro-machined flexures for their operation. For example, a flexure—typically a beam—may be made to move with respect to a fixed plate or another movable flexure to create a tunable capacitor. A switch may be provided with a flexure fixed at one end and free-floating at the other end, which is actuated by forcing the free end to move towards a substrate.
Some MEM devices require that their movable flexure or flexures be conductive. For example, the operation of a MEM tunable capacitor or current sensor, as described, for example, in U.S. Pat. No. 5,959,516 to Chang et al. and U.S. Pat. No. 6,188,322 to Yao et al., requires their movable flexures to carry respective electrical signals, such as a voltage, current, or microwave signal. Such flexures are referred to herein as “signal-carrying” flexures.
Unfortunately, there is an inherent conflict between the mechanical and electrical requirements of a signal-carrying MEM flexure. To minimize the amount of energy required to move a flexure, a small spring constant (k) is required. A small spring constant is achieved by using a long and narrow flexure. However, such a flexure will have a small cross-sectional area; as such, the flexure is likely to have a relatively high resistance (which is directly proportional to cross-sectional area) and inductance. A high flexure resistance can give rise to power dissipation and thermal management problems, and lower Q and self-resonance issues if used in RF applications. A flexure's ability to accommodate a desired current density (current/area), which is a particularly important parameter in MEM current sensor applications, is also likely to be compromised with a high resistance/small spring constant flexure.